Stator of outer rotor type motor for drum type washing machine

ABSTRACT

The present invention provides an outer rotor type motor for a drum type washing machine to reduce material and weight for fabrication, simplify fabrication process, provide stable assembly of a stator to a fixing side, such as a tub or a bearing housing, prevent unwinding of stacked steel plates in assembling a helical core, and reduce stress on the steel plates of the core. The present invention includes a helical core having multiple layers formed by winding steel plates in a helix starting from a bottom layer to a top layer, the steel plate having a base portion with teeth projected from the base portion, an upper insulator of an electric insulating material covered on an upper side of the helical core in a shape complementary to a shape of the helical core, a lower insulator of an electric insulating material covered on a lower side of the helical core at the time of assembly with the upper insulator having a shape complementary to a shape of a helical core, and a fastening means for at least two steel plates wound in a helix to prevent unwinding of any two adjacently stacked steel plates and prevent gaps between any two adjacent layers of the stacked steel plates.

This application claims the benefit of the Korean Application No.P2004-12996 and P2004-12997 both filed on Feb. 26, 2004, which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a drum type washing machine, and moreparticularly, to a stator of an outer rotor type BLDC motor, which isapplicable to a direct coupling type drum type washing machine.

2. Discussion of the Related Art

Generally, a drum type washing machine performs washing operation withthe aid of a drive force of a motor which spins a drum containinglaundry, detergent, and water, to cause friction between laundry andwater. The drum type washing machine causes almost no damage to thelaundry, prevents tangling of the laundry, and brings about the effectsof pounding and rubbing.

Drum type washing machines are categorized by an indirect coupling typeand a direct coupling type according to a drive system. In the indirectcoupling type, a drive force of a motor is indirectly transferred to adrum via a motor pulley and a belt wound to the drum pulley. In thedirect coupling type, a rotor of a BLDC motor is directly coupled with adrum to directly transfer a drive force to the drum.

Yet, in the indirect coupling type system that transfers the drive forceof the motor to the drum via the motor pulley and the belt wound on thedrum pulley instead of transferring the drive force of the motor to thedrum directly, energy loss occurs in the process of drive force transferand considerable noise is generated.

Hence, the direct coupling drum type washing machine using the BLDCmotor is widely used to solve the above problems of the drum typewashing machine.

FIG. 1 is a cross-sectional diagram of a direct coupling drum typewashing machine according to a related art.

Referring to FIG. 1, a tub 2 is provided within a cabinet 1, and a drum3 is rotatably provided within the tub 2.

A motor is provided to a rear portion of the tub 2. Specifically, astator 6 is fixed to a rear wall of the tub 2 and a rotor 5 encloses thestator 6 to be coupled to the drum 3 via a shaft.

A door 21 is provided to a front portion of the cabinet 1 and a gasketis provided between the door 21 and the tub 2.

A hanging spring 23 supporting the tub 2 is provided between an insideof a top portion of the cabinet 1 and an upper outer circumference ofthe tub 2, and a friction damper 24 is provided between an inside of abottom portion of the cabinet 1 and a lower outer circumference of thetub 2 to attenuate vibration of the tub 2.

FIG. 2 is a perspective diagram of a stator in FIG. 1 and FIG. 3 is aperspective diagram of a sectional core (SC) applied to the stator inFIG. 2.

A method of manufacturing a helical core according to a related art isexplained as follows.

First of all, a plurality of unit cores are fabricated by a pressingprocess of a steel plate. In doing so, each of the unit cores consistsof teeth 151, a base 150, and a protrusion 500 opposite to the teeth 151for forming a fastening hole 500 a. A plurality of the unit cores arestacked to form a plurality of assemblies. And, a plurality of theassemblies are linked in a circumferential direction to complete astator core that is so-called a sectional core.

The protrusion 500 plays a role in standing a fastening force of a boltas well as provides the fastening hole 500 a necessary for fastening astator to the rear wall of the tub.

Yet, such a method of manufacturing the stator 6 with the sectional coreSC is very complicated and brings about considerable loss of materials.

Meanwhile, a helical core, which is manufactured by helically stacking asteel plate consisting of teeth 151 and a base 150, is very useful inreducing the loss of materials and simplifying the manufacturingprocess. Yet, in manufacturing the helical core HC, the steel plateblanked like a strap needs to be helically bent. Hence, it is unable toprovide a protrusion for coupling a stator with a tub to an inside ofthe core.

If the protrusion 500 is provided to the inside of the core inmanufacturing the helical core HC, a core width of a part reserved forthe protrusion is too large to bend the core.

Accordingly, a stator structure that enables the same role of theprotrusion of the sectional core to be performed not by the core itselfbut by another portion is needed to be applicable to the helical coreHC.

Meanwhile, it is important to sufficiently secure the rigidity of theprotrusion provided with the fastening hole for securing the stator tothe tub, which is explained as follows.

First of all, in a washer that rotates a drum directly using a BLDCmotor, a stator is directly assembled to a fixing side of a rear portionof the tub. If the stator of a motor for a high capacity drum typewasher weighs over 1.5 kg and if a dewatering rotational speed is600˜2,000 RPM, a fastening portion of the stator 6 is broken due to thestator weight, the vibration of the high rotation, and the shake andtransformation of the rotor 5.

Specifically, in case that the stator is coupled with the rear wall ofthe tub of the drum type washer using the BLDC motor, a radial directionof the stator almost maintains parallel to a ground, the breakage of thefastening portion of the stator 6 to the rear wall of the tub getsworsened due to the vibration occurring on driving the washer.

Therefore, it is important to sufficiently secure the rigidity of theprotrusion provided with the fastening hole for securing the stator 6 tothe tub.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a stator of an outerrotor type motor for a drum type washing machine that substantiallyobviate one or more problems due to limitations and disadvantages of therelated art.

An object of the present invention is to provide an outer rotor typemotor for a drum type washing machine, by which a material and weightfor fabrication are reduced, by which a fabrication process issimplified, and by which a stator can be stably assembled to a fixingside such as a tub or a bearing housing.

Another object of the present invention is to provide a stator of anouter rotor type motor for a drum type washing machine, in which astator can be stably assembled to a fixing side such as a tub or abearing housing and by which the stator weighing at least 1.5 kg isapplicable to a drum type washing machine BLDC motor having a rotationalspeed over 2,000 RPM.

Another object of the present invention is to provide a stator of anouter rotor type motor for a drum type washing machine, by whichunwinding of any two adjacently stacked steel plates and gaps betweenany two adjacent layers of the stacked steel plates are prevented.

A further object of the present invention is to provide a stator of anouter rotor type motor for a drum type washing machine, by whichunwinding of any two adjacently stacked steel plates is prevented inassembling the helical core and by which stress on the steel plates isreduced to facilitate assembly of the core.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, astator of an outer rotor type motor for a drum type washing machineaccording to the present invention a helical core having multiple layersformed by winding steel plates in a helix starting from a bottom layerto a top layer, the steel plate having a base portion with teethprojected from the base portion; an upper insulator of an electricinsulating material covered on an upper side of the helical core in ashape complementary to a shape of the helical core, a lower insulator ofan electric insulating material covered on a lower side of the helicalcore at the time of assembly with the upper insulator having a shapecomplementary to a shape of a helical core, and a fastening means for atleast two steel plates wound in a helix so as to prevent unwinding ofany two adjacently stacked steel plates and prevent gaps between any twoadjacent layers of the stacked steel plates.

In this case, fastening means includes an engaging protrusion providedto each upper or lower surface of the teeth of the steel plate, and aengaging recess provided to each lower or upper surface of the teeth ofthe steel plate to correspond to the engaging protrusion.

Furthermore, the stator further comprises at least three fasteningportions formed as one body in each of the upper and the lower insulatorwhich projects from an inside of the helical core toward a center of thestator for securing the stator to a fixing side of a tub.

In another aspect of the present invention, a stator of an outer rotortype motor for a drum type washing machine includes a helical corehaving multiple layers formed by winding steel plates in a helixstarting from a bottom layer to a top layer, the steel plate having abase portion with teeth projected from the base portion, an upperinsulator of an electric insulating material covered on an upper side ofthe helical core in a shape complementary to a shape of the helicalcore, and a lower insulator of an electric insulating material coveredon a lower side of the helical core at the time of assembly with theupper insulator having a shape complementary to a shape of a helicalcore, wherein the base portion of the helical core includes slots forreducing stress during winding the core.

In this case, a central portion of each slot represents a maximum depthand depths of each slot symmetrically become smaller toward lateral sideportions away from the central portion, the depths of the lateral sideportions symmetrically becoming small enough to connect to an edge ofthe base portion.

And, each slot is provided at the base portion of the helical core andlocated between two adjacent teeth.

Moreover, the stator further includes at least three fastening portionsformed as one body in each of the upper and the lower insulator whichprojects from an inside of the helical core toward a center of thestator for fastening the stator to a fixing side of a tub.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a cross-sectional diagram of a direct coupling drum typewashing machine according to a related art;

FIG. 2 is a perspective diagram of a stator according to a related art;

FIG. 3 is a perspective diagram of a sectional core of the stator inFIG. 2;

FIG. 4 is a perspective diagram of a stator according to the presentinvention;

FIG. 5 is a projected perspective diagram of the stator in FIG. 4;

FIG. 6A is a layout of a part ‘A’ in FIG. 5;

FIG. 6B is a cross-sectional diagram of a helical core according to acutting line I-I in FIG. 6A, in which a stacked structure is shown;

FIG. 7 is a perspective diagram of a backside of an upper insulator inFIG. 5;

FIG. 8 is a layout of the stator in FIG. 4; and

FIG. 9A and FIG. 9B are front diagrams of an insulator for common use.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

One embodiment of the present invention is explained with reference toFIGS. 4 to 9 as follows.

First of all, one embodiment of the present invention is explained withreference to FIGS. 4 to 7 as follows.

FIG. 4 is a perspective diagram of a stator according to the presentinvention and FIG. 5 is a projected perspective diagram of the stator inFIG. 4.

FIG. 6A is a layout of a part ‘A’ in FIG. 5 and FIG. 6B is across-sectional diagram of a helical core according to a cutting lineI-I in FIG. 6A, in which a multi-layer structure is shown.

Meanwhile, FIG. 7 is a perspective diagram of a inside of an upperinsulator in FIG. 5, FIG. 8 is a layout of the stator in FIG. 4, andFIG. 9A and FIG. 9B are front diagrams of an insulator for common use.

Referring to the drawings, in FIG. 4 and FIG. 5, a stator 6 of an outerrotor type motor according to one embodiment of the present inventioncomprises a helical core HC having multiple layers formed by windingsteel plates in a helix starting from a bottom layer to a top layer, thesteel plate having a base portion 150 with teeth 151 projecting from thebase portion 150, an upper insulator 60 a of an electric insulatingmaterial covered on an upper side of the helical core HC in a shapecomplementary to a shape of the helical core, a lower insulator 60 b ofan electric insulating material covered on a lower side of the helicalcore at the time of assembly with the upper insulator having a shapecomplementary to a shape of a stator core, and at least three fasteningportions 600 formed as one body in each of the upper insulator 60 a andlower insulator 60 b which projects from an inside of the helical coreHC toward a center of the stator for fastening the stator 6 to a fixingside of a tub.

In this case, a plurality of slots 152 are provided to the base portion150 to reduce stress in assembling the core with a plurality of steelplates. And, each of the slots 152 is formed polygonal so that its depthsymmetrically becomes smaller from a central portion 152 a having amaximum depth H toward each lateral side portion to become zero at anedge of the base portion 150.

Furthermore, the stator 6 includes fastening means to prevent unwinding(spring-back) of any two adjacently stacked steel plates and preventgaps between any two adjacent layers of the stacked steel plates.

In this case, the fastening means, as shown in FIG. 6A and FIG. 6B,includes a engaging protrusion 154 a provided to each upper surface ofthe teeth 151 of the steel plate and a engaging recess 154 b provided toeach lower surface of the teeth 151 of the steel plate to correspond tothe engaging protrusion 154 a.

Alternatively, it is a matter of course that the engaging protrusion 154a is provided to each lower surface of the teeth 151 of the steel plateand the engaging recess 154 b is provided to each upper surface of theteeth 151 of the steel plate to correspond to the engaging protrusion154 a.

A fastening portion 600, as shown in FIG. 5, has a fastening hole 620 afor securing the stator 6 to a fixing side, such as a tub, with afastening member. The fastening hole 620 a is formed by a boss 620projected to the back side of the fastening portion 600.

A support rib 650 is provided on an inside along a circumferentialdirection thereof in contact with the helical core for supporting aninside surface of the helical core HC in each of the upper insulator 60a and lower insulator 60 b.

Furthermore, the fastening portion 600 of each of the upper insulator 60a and the lower insulator 60 b includes at least one reinforcing rib 660connected between the boss 620 of the fastening hole 620 a and thesupporting rib 650 for spreading fastening force concentrated on theboss 620 and reinforcing a strength of the fastening portion 600.

As shown in FIG. 7, the fastening portion 600 of each of the upperinsulator 60 a and the lower insulator 60 b has a reinforcing rib 670 atan inside circumference thereof, and at least one connection rib 680connected between the reinforcing rib 670 and the supporting rib 650which supports an inside surface of the core in a radial direction, forproviding a supporting force.

The reinforcing rib 670, together with the reinforcing rib 660, connectsbetween the bosses 620 having fastening holes of the upper insulators 60a and the lower insulators 60 b to spread the fastening forceconcentrated on the boss, and reinforce a strength of the fasteningportion 600.

Each of the upper insulator 60 a and the lower insulator 60 b has tips610 a on opposite sidewalls of each of the teeth 610 thereof havingshapes in complementary to each other for fitting in at the time ofassembly to form a flush surface.

In this case, if one of the tips 610 a and 610 b has a ‘┐’ shape, theother has a ‘└’ shape.

At the opposite end surfaces substantially perpendicular to the oppositesidewall surfaces of the teeth 610 of the upper insulator 60 a and thelower insulator 60 b, there are tips 610 a and 610 b having shapes incomplementary to each other.

The teeth 610 of each of the upper insulator 60 a and the lowerinsulator 60 b has a seating surface 611 a at an end for seating a coreshoe 151 a of the helical core HC.

Along with this, in the vicinity of the fastening hole 620 a of thefastening portion 600 of the upper insulator 60 a, there is apositioning projection 630 having a shape in complementary to apositioning hole or a slot (not shown) in the fixing side of the tub.

Moreover, there is a cylindrical sleeve 800 in the fastening hole 620 a,a spring pin having an elasticity owing to an incised portion, or ahollow pin enabling press fit in the fastening hole 620 a, serves as abushing.

Furthermore, the fastening hole 620 a of each of the upper insulator 60a and the lower insulator 60 b has a land around the fastening hole 620a for preventing the bolt head from being brought into direct contactwith the cylindrical sleeve 800 at the time of bolt fastening.

The base portion 150 has slots 152 for reducing stress at the time ofwinding in formation of the core to make winding easy, and the multiplelayers thereof are fastened with rivets 153 passed through pass throughholes in the base portion 150.

A winding beginning portion or a bottom layer of the helical core HC anda winding end portion or a top layer of the helical core HC can bewelded to predetermined contact portions of the base portion 150.

Referring to FIG. 8, the stator 6 according to the present inventionincludes at least three fastening portions 600 formed as one body ineach of the upper insulator 60 a and the lower insulator 60 b whichprojects from an inside of the helical core toward a center of thestator for fastening the stator to a fixing side of a tub.

If a length of each of the teeth 151 projected from a lateral outside ofthe helical core HC is set to ‘a’ and if a distance from a lateralinside of the helical core to a center of the fastening hole of thefastening portion 600 is set to ‘b’, the fastening portion 600 is formedto meet a definition of ‘a≧b’.

Meanwhile, a reference number ‘8’ in FIG. 5 indicates a hole sensorassembly for a motor control and a reference number ‘9’ indicates a taphousing assembly for power connection to supply power to the statorside.

An operation of the above-configured present invention is explained asfollows.

First of all, the helical core HC, which is formed by winding steelplates in a helix starting from a bottom layer to a top layer, the steelplate having a base portion 150 with teeth 151 projected from the baseportion 150, is used as the core configuring the stator. Hence, thepresent invention does not need the processes of assembling and weldingunit cores for the sectional core SC, thereby simplifying thefabricating process.

And, the helical core HC according to the present invention has not theprotrusions of the sectional core, thereby reducing the material loss.

Namely, the method of fabricating the stator according to the presentinvention is simplified and reduces the material loss.

The fastening means, which include the engaging protrusions 154 a andthe engaging recesses 154 b, are provided to the teeth 151 of the steelplate wound in a helix to prevent unwinding of joined steel plates andprevent gaps between layers of the stacked steel plates, therebyfacilitating the accurate core fabrication.

The polygonal recesses 152 are provided to the base portion 150 of thesteel plate configuring the helical core HC to prevent the unwinding ofthe steel plate by reducing the stress of the base portion 150 inwinding the steel plate and to facilitate the winding work of the steelplate for the formation of the helical core HC.

Moreover, the stator 6 of the present invention has sufficient rigidityagainst the fastening force of the bolt in a manner of improving thestructure of the upper and lower insulators 60 a and 60 b withoutforming the protrusion for standing the fastening force in fixing thestator 6 to the core itself.

That is, by providing structures that work the same with the projectedportion of the division core to the fastening portions 600 of the upperinsulator 60 a and the lower insulator 60 b, a stator 6 can be provided,to which the helical core HC is applicable.

Moreover, spaces 640 between the ribs 650, 660, 670, and 680 at a backside of the fastening portion 600 dampen and attenuate vibrationoccurred during driving the motor, to improve mechanical reliability ofthe stator 6, and contributes to the reduction of the insulatormaterial.

The supporting ribs 650 of the upper insulator 60 a and the lowerinsulator 60 b formed at an inside in contact with the helical core HCalong the circumferential direction support an inside of the helicalcore HC.

The reinforcing rib 660 connected between the boss 620 of the fasteninghole 620 a and the supporting rib 650 at each of the fastening portion600 of the upper insulator 60 a and the lower insulator 60 b spread thefastening force concentrated on the boss 620, and reinforces a strengthof the fastening portion 600.

According to this, the stator 6 can effectively prevent a fasteningportion of the stator 6 suffering from breakage caused by vibration atthe spinning, shaking and deformation of the rotor 5 even at a largecapacity drum type washing machine having a weight over 1.5 kg only ofthe stator, and a spinning speed ranging 600-2,000 RPM.

As a positioning projection 630 in the vicinity of the fastening hole620 a of the fastening portion 600 fits in a positioning hole (notshown) in the tub 2, fastening of the stator is easy.

Hence, the location setting projection 630 facilitates the stator 6according to the present invention to be coupled with the tub 2, wherebya maintenance and repair work of a serviceman can be easily done forafter-service.

Alternatively, it is a matter of course that the positioning projection630 may be formed on the tub2, and the positioning hole may be formed inthe fastening portion 600.

FIG. 9 a and FIG. 9 b are reference drawings, illustrating a versatilityof application of the insulators, wherein it can be noted that the upperand lower insulators 60 a and 60 b, respectively, are applicable even ifa total height of the helical core varies within a certain range.

That is, FIG. 9 a illustrates a case when a total height h1 of the coreis a height which permits tips 610 a and 610 b of the upper and lowerinsulators 60 a and 60 b fit exactly. FIG. 9 b illustrates a case when atotal height of the core is a height greater than a case of FIG. 9 asuch that the tips 610 a and 610 b of the upper and lower insulators 60a and 60 b are unable to fit exactly, but spaced a certain distance.

Even if the total height h2 of the core is greater than a height thatpermits the tips 610 a and 610 b of the upper and lower insulators 60 aand 60 b, respectively, fit exactly, such that there is a space betweenthe tips 610 a and 610 b, because the insulation against the core teethis still achievable; the upper and lower insulators 60 a and 60 b areapplicable to the case of FIG. 9 b, too.

Thus, since the separate type upper and lower insulators of theembodiment are applicable to the core regardless of the total height ofthe core within a certain range of the total height, the separate typeupper and lower type insulators of the embodiment can improveworkability on an assembly line.

Besides, the slot provided to the core are polygonal is polygonal in theabove description of the present invention. Yet, the slot can besemicircular or oval to reduce the stress and to facilitate the windingwork on the core formation.

Accordingly, the present invention provides the following effects oradvantages.

First of all, the material and weight for fabrication of the stator ofthe drum type washing machine BLDC motor are reduced, the fabricationprocess is simplified, and the stator can be stably assembled to thefixing side such as a tub.

Specifically, the stator can be stably assembled to the fixing side suchas a tub or a bearing housing like the case of applying the sectionalcore despite the reduction of the materials of the helical core andinsulator, whereby the stator weighing at least 1.5 kg is applicable toa drum type washing machine BLDC motor having a rotational speed over2,000 RPM.

Secondly, the stator is facilitated to be assembled to the tub in theassembly line, whereby a maintenance and repair work of a serviceman canbe easily done for after-service.

Thirdly, the present invention facilitates the prevention of theunwinding of adjacently stacked steel plates, the prevention of gapsbetween adjacent layers of the stacked steel plates, and the fabricationby employing the helical core to perform the winding work for the coreformation with ease, and enhances the mechanical reliability andendurance by raising the rigidity of the fastening portion of the statorto reduce the noise and vibration.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A stator of an outer rotor motor for a drum washing machine,comprising: a helical core having multiple layers formed by winding asteel plate in a helix starting from a bottom layer to a top layer, thesteel plate having a base portion with teeth projected from the baseportion; an upper insulator of an electric insulating material coveredon an upper side of the helical core in a shape complementary to a shapeof the helical core; a lower insulator of an electric insulatingmaterial covered on a lower side of the helical core at the time ofassembly with the upper insulator having a shape complementary to ashape of a helical core; and fastening means for preventing unwinding ofany two adjacently stacked layers and preventing gaps between any twoadjacent layers, the fastening means including an engaging protrusionprovided on each upper or lower surface of the teeth of the steel plate;and an engaging recess provided on each lower or upper surface of theteeth of the steel plate to correspond to the engaging protrusion. 2.The stator of claim 1, wherein the fastening means is provided to eachof the teeth of the steel plate.
 3. The stator of claim 1, furthercomprising at least three fastening portions formed as one body in eachof the upper and the lower insulator which project from an inside of thehelical core toward a center of the stator for fastening the stator to afixing side of a tub.
 4. The stator of claim 3, wherein a fastening holeis provided in each of the at least three fastening portions to securethe stator to a tub wall with fastening members.
 5. The stator of claim4, wherein the fastening hole in the fastening portion is constructed ina boss projected toward a back side of the fastening portion.
 6. Thestator of claim 1, wherein each of the upper insulator and the lowerinsulator includes a supporting rib on an inside along a circumferentialdirection thereof in contact with the helical core for supporting aninside surface of the helical core.
 7. The stator of claim 6, whereinthe fastening portion of each of the upper insulator and the lowerinsulator includes at least one reinforcing rib connected between theboss of the fastening hole and the supporting rib for spreadingfastening force concentrated on the boss and reinforcing a strength ofthe fastening portion.
 8. The stator of claim 1, wherein each of theupper insulator and the lower insulator includes tips on oppositesidewalls of each of tooth covers thereof, the tips of the upperinsulator having shapes complementary to the corresponding tips of thelower insulator for fitting together at the time of assembly to form aflush surface.
 9. The stator of claim 8, wherein the tips on oppositesidewalls of each of the tooth covers include ‘└’ shape if the otherside of the upper, and lower insulators includes a ‘┐’ shape.
 10. Thestator of claim 1, further comprising tips having shapes symmetrical toeach other at opposite end surfaces substantially perpendicular toopposite sidewall surfaces of tooth covers of the upper insulator andthe lower insulator.
 11. The stator of claim 1, wherein tooth covers ofeach of the upper insulator and the lower insulator include a seatingsurface at an end for seating a core shoe of the helical core.
 12. Thestator of claim 1, wherein the insulator includes a positioningprojection in the vicinity of the fastening hole thereof having a shapecorresponding to a positioning hole or a slot on a fixing side of a tub.13. The stator of claim 12, further comprising a cylindrical sleeve onan inside of the fastening hole.
 14. The stator of claim 13, wherein thecylindrical sleeve is a spring pin having elasticity owing to a portionincised along a length direction of an outside surface.
 15. The statorof claim 13, wherein the cylindrical sleeve is a hollow pin press fit inthe fastening hole, the cylindrical sleeve having no incised portion.16. The stator of claim 1, wherein the base portion of the helical coreincludes slots for reducing stress during winding the core.
 17. Thestator of claim 16, wherein a central portion of each slot represents amaximum depth and depths of each slot symmetrically become smallertoward lateral side portions away from the central portion, the depthsof the lateral side portions symmetrically becoming small enough toconnect to an edge of the base portion.
 18. The stator of claim 16,wherein each slot is provided at the base portion of the helical coreand located between two adjacent teeth.
 19. The stator of claim 1,wherein the multiple layers are fastened by rivets passed through passthrough holes in the base portion.
 20. The stator of claim 1, whereinthe bottom layer and the top layer of the helical core are welded topredetermined portions of the base portion, respectively.
 21. The statorof claim 1, wherein if a length of each of the teeth projected from alateral outside of the helical core is set to ‘a’ and if a distance froma lateral inside of the helical core to a center of a fastening hole ofa fastening portion is set to ‘b’, ‘a’ is equal to or greater than ‘b’(a≧b).
 22. The stator of claim 1, wherein each of the teeth includes atooth main body and a tip at an end of the tooth main body, and theengaging protrusion and the engaging recess are located at a middleportion of an upper or lower surface of the tooth main body.